Ultrasonic Inspection of an Underwater Piping System Covered with Thick Coating

Abstract

The largest oil production field in Venezuela is located in the Maracaibo lake, where 900,000 barrels are extracted daily. As part of the production system there exist 20,000 kilometers of underwater pipes, which transport crude oil, natural gas, and water among thousands of production platforms. One important problem faced in the maintenance of this complex system of pipes is the wall thickness loss caused by corrosion and/or erosion from the inside of the pipes [1]. Even though the occurrence of these two phenomena have been somehow reduced in the last five years, the problem of monitoring the wall thickness still remains. In this regard, the pipes at the Maracaibo lake present a unique condition that is not share by any other piping system in the international oil industry: the pipes are coated with thick layers of polyethylene or vulcanized neoprene, depending on their location or their depth below the lake level, in order to avoid external corrosion caused by the highly aggressive waters of the lake. Although, ultrasonic underwater inspection systems have been applied in the offshore oil industry for many years to inspect platform structures and piping systems, an ultrasonic inspection procedure capable to inspect underwater piping system covered with thick coatings of polyethylene or neoprene has not yet been developed. In this work we present an ultrasonic method capable of measuring the thickness of the pipe through the protective coatings.